1) Field of the Invention
The invention relates to an automatic initial-cutting device for microtomes, particularly ultramicrotomes, with an object or knife moved by a driving motor. A feed movement is produced by a servomotor by way of relative movement between the knife edge and the object in order to produce sections and by at least one sensor for determining the forces resulting from separation of the sections or variations in the system which are brought about by these forces.
2) State of the Prior Art
According to the state of the art, when a microtome, particularly an ultramicrotome, is in use, considerable problems occur in connection with bringing the knife up to the object, or vice-versa. Even with enlarged viewing of the object-knife area through a microscope, which is normal on ultramicrotomes or semi-thin sectioning appliances (see in this respect H. Sitte, Ultramicrotome mta-journal extra No. 10, Umschau-Verlag Breidenstein GmbH, 1985 and; H. Sitte and K. Neumann, Ultramikrotome und apparative Hilfsmittel fuer die Ultramikrotomie, in G. Schimmel and W. Vogell, Methodensammlung der Elektronen-mikroskopie, Wissenschaftliche Verlags-GmbH Stuttgart, 1983, delivery 11), it is possible only with difficulty to achieve a binding assessment of the relative position between the object or specimen and the knife edge in the cutting area of object movement or knife movement. Problems result from the parallax error due to the fact that the optical axis of a stereo microscope is usually inclined to the path of the moving element and from the surface of the specimen, which is often irregular prior to the first cut, and from the frequently curved path of the moving part and from the general difficulty of estimating the spatial location of the moving part (e.g. the object) in relation to the fixed part (e.g. the knife edge). The result of this uncertainty is frequently either damage to the specimen and/or the knife edge upon an unintended contact between the two parts. During a first rotation ("cutting cycle") by the knife edge, a considerably too thick section may be taken from the specimen. In the event that an excessively cautious adjustment, and thus an excessively great distance between the knife edge and the object path, or vice-versa, between the area of the object on which the initial cut is to be made and the knife path, an unjustifiably large number of unsuccessful cutting cycles and thus an unjustifiably long waiting time are required from the commencement of motor movement to the taking of the first section by the knife. If the above-mentioned waiting time results, for obvious reasons, in a serious strain on the user, and in a waste of valuable working time, then as a result of the first-mentioned error, damage frequently occurs which cannot be repaired. This applies both to the damage to valuable individual objects which are often the outcome of months of preparation, or damage to valuable cutting edges, for example the valuable diamond cutting edges currently used mainly for taking ultra-thin sections.
In order to as far as possible exclude the possibility of damage or unjustifiably long waiting times, it is conventional in the state of the art to employ special feeding aids (e.g. underfloor lighting to allow adjustment by reflection) and to increase the travelling speed of the moving object or knife and/or to increase the rate of feed until the first section fragment is obtained. However, even these measures are only successful in part, because the cutting area prior to the initial cut is, in most cases, irregularly formed, and does not therefore permit of adjustment by reflection. This is because an increase in the travelling speed of the moving part makes observation of the processes even more difficult by casting shadows on the knife edge or the movement of the knife edge itself as the speed increases. Finally, there are limits to how much the rate of feed can be increased, due to the stability of the knife edge or of the specimen. In particular, with increasing the travelling speed and the rate of feed, it becomes increasingly more difficult for the user to vary both parameters at the right time after creating the first section fragment in such a way that the possibility of damage to the knife edge and/or the specimen, as a result of pieces being broken or torn away, can be reliably obviated.